Within the field of watchmaking, a strike mechanism can be combined with a conventional timepiece movement to act as a minute repeater or to indicate a programmed alarm time. This type of strike mechanism generally includes at least one gong made of metallic material, such as steel, bronze, precious metal, metallic glass, sapphire or quartz. This gong may describe, for example, at least one portion of a circle around the timepiece movement in the watch frame. The gong is secured via at least one end thereof to a gong-carrier, which is itself integral with a watch plate. A hammer of the mechanism is rotatably mounted on the plate, for example in proximity to the gong-carrier, so as to strike the gong to make it vibrate. The sound produced when the hammer strikes the gong is within the audible frequency range from 1 kHz to 20 kHz. This indicates a well-defined time, programmed alarm or minute repeater to the person wearing the watch.
As shown in EP Patent No. 1 574 917, the strike mechanism of a watch may include two gongs secured via one end thereof to the same gong-carrier, which is itself integral with a plate. Each gong can be struck by a respective hammer. To achieve this, each hammer is driven by its own drive spring, which has to be pre-wound, so as to drive the hammer against the gong to indicate a minute repeater or alarm time. Two damping countersprings are provided for pushing back the hammers and holding them at a distance from the gongs in the idle mode. The damping countersprings also slow down the fall of each hammer prior to striking the respective gong before pushing each hammer back into the idle position. Eccentrics are also provided for regulating the operation of the countersprings to prevent each hammer bouncing against the respective gong.
One drawback of this type of strike mechanism structure with countersprings is that there is a significant waste of kinetic energy from the hammer when the respective gong is struck, which reduces the acoustic level of the strike work. Moreover, even if the pre-winding of the drive springs is increased, this means adapting the countersprings via their eccentric to prevent any bouncing, which is another drawback of this type of strike mechanism.
EP Patent No. 2 048 548, which mainly discloses a hammer for a watch strike mechanism, may also be cited. This hammer has two parts hinged to each other and a resilient element secured to one of the hinged parts. When the hammer is in a stable position, the resilient spring element holds the two parts of the hammer, whereas when the hammer is in the strike position, the two parts move away from each other, returned by the resilient spring element. With this arrangement, it is possible to reduce the kinetic energy wasted by the hammer against a damping member. However, in order to be able to prevent the hammer wasting energy when it strikes the gong, this hammer arrangement makes the strike mechanism more complicated to make, which is a drawback. The hammer may bounce against the gong in an undesirable manner during striking, which is another drawback.